>> "A false positive is an alert that triggers on normal traffic where no
>> intrusion or attack is underway"
>
> That's a good definition, but not really complete. Under that
> definition, if you place a rule that flags IRC connections, and it
> fires, is that a false positive?

GH: No. If a rule or signature fires on traffic you asked it to fire on,
then it is not a false positive, regardless of whether or not it is an
attack or intrusion.

>
> Is it a false positive a case where there is no rule, or the traffic
> does not match with the rule, and the engine still fires?

GH: Yes.

> Is it a false positive a case where a rule correctly matches, but the
> user didn't want to be alerted to that traffic ?

GH: Some say yes, some say no. I am one of those who says this is not a
false positive. Perhaps this is a misconfiguration of the sensor, but it is
still doing what it was asked to do. I wrote "Security Monitoring with
CS-MARS" for Cisco Press, and that product considers this to be a false
positive.

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